The abdomen is the middle part of the human body located between the thorax and pelvis. The abdominal wall covers a large area and encloses the abdominal cavity. The abdominal wall is bounded superiorly by the xiphoid process and costal margins, posteriorly by the vertebral column and inferiorly by the upper parts of the pelvic bones. It can be divided into anterolateral and posterior sections. The wall consists of multiple layers, the most superficial one being skin.

Besides the skin, there are six more layers:

  • subcutaneous fat,
  • superficial fascia,
  • muscles,
  • transverse fascia,
  • extraperitoneal fat and
  • parietal peritoneum.

The skin is echogenic when investigated with ultrasound. The subcutaneous fat is usually hypoechoic. The muscles reveal medium-level echoes with a lamellar pattern of the muscle fibers.

The superficial fascia represents connective tissue, and its composition depends on its location. Above the umbilicus, there is a single sheet of connective tissue that is continuous with the superficial fascia in other regions. Below the umbilicus, fascia is divided into two layers. The superficial layer is also called Camper’s fascia – a fatty layer that varies in thickness. The deeper layer, firmly attached to the white line (linea alba) and pubic symphysis (symphysis pubis), also called Scarpa’s fascia, is membranous and contains little to no fat. Vessels and nerves run between these two layers.

There are five muscles of the anterolateral abdominal wall, which can be divided into two groups. The muscles of the flat group (external oblique, internal oblique, and transverse abdominis) are all situated on either side of the abdomen and have fibers that begin posterolaterally and are replaced by an aponeurosis on the frontal part. The lower part of the external oblique aponeurosis forms the inguinal ligament on each side. There are two vertical muscles near the midline – rectus abdominis and pyramidalis muscle. The whole physique of the abdominal muscles plays an essential role in maintaining many normal physiological functions.

Ultrasound examination

The skin is echogenic when investigated with ultrasound. The subcutaneous fat is usually hypoechoic. The muscles reveal medium-level echoes with a lamellar pattern of the muscle fibers. The normal skeletal muscle shows a lamellar pattern, a relatively hypoechoic background reflecting muscle fascicles and clearly demarcated linear hyperechoic strands related to fibroadipose septa (Perimysium).

Layers of the abdominal wall.

Available at: https://i1.wp.com/www.anatomyqa.com/wp-content/uploads/2017/04/layers-of-anterior-abdominal-wall.png?resize=736%2C338 (Accessed: 7 March 2020).

Layers of the abdominal wall.

Available at: https://i.pinimg.com/originals/82/c6/78/82c678f9ab612de67a6b0b0b6ae40418.png (Accessed: 7 March 2020).

Muscles of the abdominal wall.

Available at: https://antranik.org/wp-content/uploads/2011/10/muscles-of-the-abdominal-wall.jpg (Accessed: 7 March 2020).

Anterior abdominal wall.

Available at: https://accessmedicine.mhmedical.com/data/books/1057/p9780071798938-ch002_f002.png (Accessed: 7 March 2020).

Anterior abdominal wall – ultrasound image.

Available at: https://abdominalkey.com/wp-content/uploads/2017/01/A303475_1_En_6_Fig4_HTML.jpg (Accessed: 7 March 2020).

Anterior abdominal wall – panoramic ultrasound image PAME Maribor
Probe movement when assessing abdominal wall
Ultrasound image of rectus abdominis muscle and linea alba, transverse view PAME Maribor 1-5
Ultrasound image of rectus abdominis muscle and linea alba, sagittal view PAME Maribor

We can palpate some of the organs or visualize their position by surface markings through the abdominal wall. The abdomen is split into nine regions or four quadrants for easier orientation and description of the location of pain, viscera, and surgical procedures. The regions are formed by two horizontal and two vertical planes. The quadrants are formed with one vertical and one horizontal line. The most visible structure is the umbilicus, the scar of the site of attachment of the umbilical cord.

9 Regions of the abdomen

Available at: https://media.proprofs.com/images/QM/user_images/232839/2246483622.jpg (Accessed: 7 March 2020).

Hernia

A herniaoccurs when an organ or fatty tissue squeezes through a weak spot in a surrounding muscle or connective tissue called fascia. For example, the intestines may break through a weakened area in the abdominal wall. Hernias are most common in the abdomen, but they can also appear in the upper thigh, belly button, and groin areas. Most hernias are not immediately life-threatening, but they do not disappear on their own.

Abdominal wall hernias include:

  • umbilical hernias,
  • epigastric hernias,
  • incisional hernias,
  • femoral hernias,
  • inguinal hernias.

Hernias are caused by a combination of muscle weakness and strain. Depending on its cause, the hernia can develop quickly or progressively over time.

Common causes of muscle weakness include:

  • failure of the abdominal wall to close properly in the womb, which is a congenital defect,
  • age (chronically weakens the abdominal wall),
  • chronic coughing (increases intraabdominal pressure),
  • damage from injury or surgery (acutely weakens the abdominal wall).

Factors that strain the body and may cause a hernia, especially if the muscles are weak, include:

  • being pregnant (increases intraabdominal pressure or as a complication of a C-section),
  • being constipated, which causes increased strain when having a bowel movement (increases intraabdominal pressure),
  • lifting heavy objects (increases intraabdominal pressure),
  • fluid in the abdomen, or ascites (increases intraabdominal pressure),
  • suddenly gaining weight (weakens the abdominal wall),
  • surgery in the area,
  • persistent coughing or sneezing (weakens the abdominal wall because of the constant increase in the intraabdominal pressure). (5)
Abdominal wall hernias

Available at: https://www.uptodate.com/contents/images/PI/87588/Abdominal_hernias_PI.jpg (Accessed: 7 March 2020).

Spigelian hernia

Rumack, C. M. and Leṿin, D. (2017) Diagnostic ultrasound. Elsevier.

Incarcerated inguinal hernia with visible intestine outside abdominal cavity PAME Maribor
Scheme of the umbilical hernia

Available at: https://wasurgery.com.au/images/har1.png (Accessed: 7 March 2020).

Umbilical hernia

Rumack, C. M. and Leṿin, D. (2017) Diagnostic ultrasound. Elsevier.

ULTRASOUND EXAMINATION

How to correctly assess an inguinal or femoral hernia can be seen in the following video.

When the protruding abdominal contents can be pushed back in gently, the hernia is said to be reducible. If returning the contents back in is not possible, we refer to this type of hernia as non-reducible or incarcerated. The incarcerated hernia can lead to the blood supply of the intestinal tissue being cut off. When this occurs, the hernia is said to be strangulated. It can cause the tissue to die, inflicting severe pain at the site of the hernia accompanied by nausea and vomiting due to the obstruction of the intestines. This situation is a surgical emergency requiring an urgent operation because of the risk of gangrene. The early surgical intervention of the strangulated hernia with obstruction is crucial as the delayed diagnosis can result in the need for bowel resection with prolonged recovery and increased complication rate. Strangulated hernias may lead to bacterial translocation and intestinal wall necrosis (potentially resulting in bowel perforation).

Symptoms of a hernia in need of emergency treatment include:

  • severe pain, swelling or redness at the hernia site,
  • hernia bulge growing quickly,
  • nausea and/or vomiting,
  • constipation and/or bloating,
  • fever

Hernias that cause no symptoms and can be easily pushed back in may be treated without surgery.

Ventral hernia and strangulated hernia

Available at: http://www.tkclaw.com/wp-content/uploads/2018/10/Hernia-Strangle.png (Accessed: 7 March 2020).

Resources

Gray, H., Carter, H. V. (Henry V. and Davidson, G. (2013) Gray’s Anatomy. Arcturus Publishing Ltd.

Draganić, V. et al. (2005) Anatomija ćoveka : prirućnik za praktićnu nastavu : [za studente medicine]. Beograd: IŠP ‘Savremena administracija’.

The Anterolateral Abdominal Wall - Muscles - TeachMeAnatomy. Available at: https://teachmeanatomy.info/abdomen/muscles/abdominal-wall/ (Accessed: 9 March 2020).

Anterior abdominal wall | Radiology Reference Article | Radiopaedia.org. Available at: https://radiopaedia.org/articles/anterior-abdominal-wall (Accessed: 8 March 2020)

Hernia: Causes, Treatment, Types, Prevention, Symptoms & More. Available at: https://www.healthline.com/health/hernia#symptoms (Accessed: 7 March 2020).

Rumack, C. M. and Leṿin, D. (2017) Diagnostic ultrasound. Elsevier.

Birindelli, A. et al. (2017) ‘2017 update of the WSES guidelines for emergency repair of complicated abdominal wall hernias’, World Journal of Emergency Surgery. BioMed Central Ltd., pp. 1–16. doi: 10.1186/s13017-017-0149-y.